283 heads on a 305

[john46]

Anyone ever try 283 power pack heads on a 305 block? I am not looking for high performence. I want to put a small block in my 46 1/2 ton pickup. I want good performence and good MPGs. I already the motor and the heads and don't want to spend a lot o money.

[MagicRat]

I think the compression will be .75 higher than the 283 compression, so you will need premium fuel, or else it will ping like crazy.

The 305 bore is smaller than a 283, so, depending on the 283 valve size, you may get power-robbing valve shrouding, or possibly wall interference.

The 283 heads probably do not have hardened valve seats, so you may need a lead additive, or you might get valve seat recession.

So... I think you will get no extra power over a 305 head, but you will have the privilege of spending extra money for premium fuel.

Hopefully, MrPbody will weigh in and tell you all the things I missed

[john46]

Thanks Magicrat,
The heads were on the block when I got a hold of it. They are in pretty good shape. I did some research and it seems the best heads for a 305 have a casring number ending in 416. The 305 seems like a good choice, I don't need a lot of power but, I want good gas milage.

[777stickman]

Another thing to consider is that the 283 heads are probably not drilled and tapped for accessory mounting holes.

[MrPbody]

The 416s are the "run of the mill" 305 heads. Not a bad head, nothing "to write home about". The "good" 305 head is the 601 casting. It has the larger 1.84" valves (like 416) and a very small combustion chamber (58 CCs IIRC). It was determined by Chevorlet the 1.84" valve is "optimum" for the 3 3/4" bore size.

283 heads are okay. Just that. They were designed in the 1950s. The 305 heads are from the '70s. More efficient. "Thinner" though, so be sure to have them checked for cracks. NOTE: they're only "prone" to cracking if over-heated, not in "regular service".

IMO, 305 heads would be preffered.

Jim

[john46]

Thanks Jim,
I appreciate the info. I will look into 601 casting heads. Iam thinking of a preformer manifold (Edlebrock), mild cam and small 4 brl carb.
John

[john46]

By the way Jim, what are IMO heads

[MrPbody]

IMO = "In my opinion"....

Performer is an excellent choice for the smaller engine. A well built Q-Jet would be the carb of choice. "Remans" should be avoided.

Consider Comp XE262H for an aggressive sounding cam. It will "act" like a bit bigger cam than when used in 350. XE256H is also very good, especially if a "smooth" idle and stock converter are called for.

Jim

[john46]

Thanks again Jim, Iam new to forums. I don't know all the jargon.

[Blue Bowtie]

If you have difficulty finding '601s in serviceable condition you can use the '416 (14014416) heads. As cast, the '601 heads generally flow a bit better and have a bit more runner volume. However, with a little port work the '416s will outflow the '601s in stock form, and they also had 58cc chambers.

If you have a little time and a die grinder and carbide burrs, you can use these templates to get the '416s flowing fairly well while still maintaining the kind of port velocity you need for the smallish 305:



Regardless of which head you select, valve shrouding is a problem in either of these castings. Even with the 1.84 valves the tight chambers create a shrouding issue. If you can't stack at least 0.080" of shim between the valve perimeter and the chamber wall, that portion of the valve is all but useless.



I feel it is far better to add a few CCs of chamber volume to insure perimeter flow than to try to maintain a higher static CR and ignoring the shrouding. Even with more chamber volume, the true, dynamic CR will be higher and power/efficiency will be improved by opening the chamber to allow full perimeter valve flow. You can also improve perimeter flow with a radius on the front (face) side of the valve as much as with a multi-angle seat grind.

And cam selection will be crucial. The factory, despite all our lambasting, seemed to know exactly what it was doing when it installed all those "peanut" cams in 305s. The measured head flows didn't improve much at all above 0.400" lifts, so a higher lift cam does almost nothing with stock heads. It is more important to get the valves opened and closed as quickly as possible to the 0.350-ish range than to open them to 0.550" where flow is really not significantly better than at 0.400":



If you perform some head work the flows improve at higher lifts, but again the increase in flow beyond 0.450" is negligible, and it is far more important to plot the time under the curve than to consider peak lift as the determining factor in selection.

[john46]

Thanks Blue Bowtie
Would a heavier (thicker) head gasket serve the same purpose as a shim?
John

[MrPbody]

No, the gasket won't "help". The area nearest the cylinder wall is where the mixture comes flying down the runner and "slams" into it.

Blue Bowtie is correct. "Unshrouding" the intake valve will improve power more than "saving" the small amount of compression "lost" to chamber mods. We use a "Mira" cutter to open the area around the valve.

Jim